new style constraints implementation support

diff --git a/libasn1parser/asn1p_constr.h b/libasn1parser/asn1p_constr.h
index 19099b2..d375678 100644
--- a/libasn1parser/asn1p_constr.h
+++ b/libasn1parser/asn1p_constr.h
@@ -59,6 +59,8 @@
 	int _lineno;	/* Position in a source file */
 } asn1p_constraint_t;
 
+/* Human-readable constraint type description */
+char *asn1p_constraint_type2str(enum asn1p_constraint_type_e);
 
 /*
  * Constructors and a recursive destructor.